Optical detector for the presence of gas bubbles in a liquid

ABSTRACT

The invention concerns a method for detecting gas bubbles in a liquid adapted to a device comprising a light source, a light detector and a data controlling and processing unit connected to a client system comprising the following steps: emitting light from the light source, acquiring successive measurements of the light intensity sensed by the light detector and calculating a variation between two successive measurements of said light intensity. In accordance with a first embodiment of the invention, the method further comprises a step which consists in comparing the variation between two successive measurements of light intensity to a threshold S. Advantageously, a warning counter is incremented by a value A when variation between two successive measurements is higher than the threshold S and decremented by a value B in the opposite case. A proportion of bubbles higher than a maximum authorized rate is detected when said warning counter exceeds a warning value C. In a second embodiment of the invention, the method further comprises a step which consists in calculating an average value between the variations between two successive measurements of light intensity. The client system is made aware of said average value proportional to said bubble content in the liquid.

The invention concerns the domain of optical detectors for the presenceof gas bubbles in a liquid.

The invention can be utilised nonexclusively for detection of gasbubbles in a water circuit for cooling an internal combustion engine ofa motor vehicle.

It is well known to detect the presence of gas bubbles present forexample in a cooling system by means of a light source, a light detectorand a conversion device producing a signal in response to the quantityof light originating from the light source and received by the detector.

The document WO 98/55849 describes a device for detecting a gas leak ina cooling system by utilising means for detection of the presence of gasbubbles.

The device used in the document WO 98/55849 comprises a light sourcealigned with a light detector such that the source and the detector areoptically coupled via an optical path, the latter being defined by thetrajectory borrowed by the light between its emission by the source andits reception by the detector. A conversion device, connected to thelight detector, produces an electronic signal in response to thequantity of light received by the light detector and originating fromthe light source.

This device compares the electronic signal in response to the quantityof light received by the light detector to a reference signalcorresponding to the quantity of light received by the detector when theoptical path is not obstructed by the passage of a bubble. If thisdifference is superior to a predetermined threshold value, then thepassage of a gas bubble across the optical path is detected. This devicemakes it possible to detect the presence of gas bubbles in the coolingsystem, a sign of the presence of a leak in said cooling system.

This mode of comparison to a reference value does however have a numberof drawbacks.

First of all, it consists of a mode of detection such that the responsetime to the presence of bubbles is uniform. The presence of asignificant quantity of bubbles is thus detected just as rapidly as thatof a small quantity. However, small quantities of bubbles are to beanalysed more finely to ensure that detection is founded and to preventan alarm from being triggered unnecessarily.

Moreover, the reference value is fixed in time. The system has opticaldeviations (soiling, opacification, etc.) and undergoes variations intemperature such that its properties are modified over the course oftime. The sensitivity of the system is then altered and it is possiblethat after a certain time bubbles are not detected and that thecorresponding alarm is therefore not triggered. It is likewise possiblethat a small quantity of bubbles is considered as being too importantand that a false alarm is then triggered.

An aim of the invention is to propose an optical detection device forthe presence of bubbles which is both simple, economical and reliable,while rectifying the drawbacks of the abovedescribed systems.

For this purpose, the invention proposes a process for detection of gasbubbles in a liquid adapted to a device comprising a light source, alight detector and a data controlling and processing unit linked to aclient system comprising the steps of acquisition of successivemeasurements of light intensity originating from the light source andperceived by the light detector and calculation of the variation betweentwo successive measurements of said light intensity.

The time span between two successive measurements is very short withrespect to the time to be observed so that the sensitivity of the systemis altered significantly due in particular to the optical deviations andthe variations in temperature. As a result, the transformations of theproperties of the system during said time span between two successivemeasurements cannot distort the measurement of the variation in lightintensity between two successive measurements. The process according tothe invention, is thus insensitive to time modifications of theproperties of the system.

It is provided in a first preferred embodiment of the invention that theprocess of detecting gas bubbles in a liquid comprises, in addition, acomparison step of said variation between two successive measurements oflight intensity to a predefined threshold value S. The system used inthis preferred embodiment of the invention thus detects the presence ofa gas bubble in the liquid if the measurement of the variation betweentwo successive measurements of light intensity is greater than thisthreshold S.

It is advantageously provided within the scope of the first preferredembodiment of the invention that the data controlling and processingunit also comprises a warning counter incremented by a predefined valueA when the variation between two successive measurements of lightintensity perceived by the detector is greater than the threshold S anddecremented by a predefined value B in the opposite case. The warningcounter has, as an option, a predefined alarm value C, such that if thevalue of said warning counter exceeds the alarm value C, the clientsystem is informed that the maximum authorised bubble content has beenexceeded. The warning counter likewise has as an option a predefinedvalue D, known as the final alarm value, such that the client systemcontinues to be informed that the bubble content is greater than themaximum authorised bubble content and when the warning counter is lowerthan said final alarm value D. This embodiment rapidly makes it possibleto detect a significant quantity of bubbles and detects a small quantityof bubbles longer and more precisely.

It is provided in a second preferred embodiment of the invention thatthe process for detection of gas bubbles also comprises a calculationstep of the average value of a plurality of said variations between twosuccessive measurements of light intensity. The system used in thissecond preferred embodiment of the invention then sends this averagevalue which is representative of the gas bubble content in the liquid.

Advantageously, it is likewise provided that the data controlling andprocessing unit also comprises a control module for the light sourcecapable of controlling the polarisation value of the light source,making it possible to carry out a new calibration of the system. Thiscontrol module of the light source is especially capable of performingperiodical polarisation of the light source. It can, as an option, havea detector for exceeding a predefined polarisation threshold. With sucha threshold exceeding detector, it is possible, under certain conditionslinked to the selected optical configuration, to detect whether thesensor constituted by the source and the light detector is immersed inthe liquid or not.

Advantageously, the source and the light detector are arrangednoticeably orthogonally. The step of acquisition of the successivemeasurements of light intensity perceived by the light detector thenmakes it possible to acquire measurements of the quantity of light raysemitted by the light source which are reflected should the occasionarise during the presence of bubbles on the surface of a bubble in adirection noticeably orthogonal to the direction of incidence towardsthe light detector.

The source and the light detector can likewise be arranged substantiallyadjacently. The step of acquiring the successive measurements of lightintensity perceived by the light detector then makes it possible toacquire measurements of the quantity of light rays emitted by the lightsource which are reflected should the occasion arise during the presenceof bubbles on the surface of a gas bubble in a direction noticeablyparallel to the direction of incidence towards the light detector.

As an option, a temperature measuring element and at least one switchassociated with said temperature measuring element can be added to thedevice. Advantageously, the switch is capable of changing state duringthe detection of a gas bubble.

The data controlling and processing unit transmits, via an interfacemodule, to the client system the information on the temperature of theliquid and the presence of gas bubbles in the liquid. A high-amplitudelevel signal proportional to the temperature of the liquid when thepresence of a bubble is not detected or low level when the presence of abubble is detected is then provided to the client system on a singlewire.

As an option, a system of electrodes capable of measuring theresistivity of the ambient conditions can likewise be added to thedevice. The client system is then informed that the sensor constitutedby the source and the light detector is not immersed in the liquid whenthe electrode system identifies the ambient conditions as not beingliquid. The switch associated with the temperature element thenadvantageously changes state during detection of a gas bubble and duringthe absence of liquid. The client system can then be informed by ahigh-amplitude level signal proportional to the temperature of theliquid when the presence of a bubble is not detected and when the sensoris immersed in the liquid, or low level when the presence of a bubble isdetected or when the sensor is not immersed in the liquid.

Advantageously, the source and the light detector are arrangednoticeably face to face. The step of emitting the light then makes itpossible to emit from the light source a specific long-wave light suchthat it is strongly (reciprocally weakly) absorbed by the liquid andweakly (reciprocally strongly) absorbed by the gas constituting thebubbles. Optionally, the acquisition step of successive measurements oflight intensity perceived by the light detector can make it possible toacquire measurements of the quantity of light rays emitted by the lightsource which are deviated towards the light detector should the casearise during the presence of bubbles due to the differences indiffraction index between the liquid and the gas constituting thebubbles on the level of the surface of said bubbles.

As an option, a temperature measuring element and at least one switchlinked to said temperature measuring element can be added to the device.Advantageously, the switch changes state during the detection of a gasbubble.

The data controlling and processing unit transmits, via an interfacemodule, to the client system the information on the temperature of theliquid and the presence of bubbles in the liquid. A periodic signal issupplied to the client system on a single wire and the period of saidsignal is formed from a first phase constituted by a constant levelsignal of high amplitude proportional to the temperature of the liquidand from a second phase constituted by a train of impulses of modulatedwidth, the width of the impulses being modulated according to theaverage value of the successive variations in light intensity perceivedby the light detector.

Advantageously, the client system can be informed that the sensor is notimmersed in liquid when the polarisation value of the light sourceexceeds a predefined threshold value T, known as the polarisation alarmthreshold value.

The client system can then be informed of information on the temperatureof the liquid, the presence of bubbles in the liquid and the nonimmersion of the sensor in the liquid by a periodic signal wherein theperiod is formed by a first phase constituted by a constant level signalof high amplitude proportional to the temperature of the liquid and by asecond phase constituted by a train of impulses of modulated width, thewidth of the impulses being modulated according to the average value ofthe successive variations in light intensity perceived by the lightdetector and said width being maximum when the sensor is not immersed inthe liquid.

The invention likewise concerns a device for detecting gas bubbles in aliquid comprising light emission means, light detection means and datacontrolling and processing means linked to the light detection means,characterised in that following the emission of light by the lightemission means and detection of light by the light detection means, thedata controlling and processing means are capable of obtaining lightdetection means of the successive measurements of light intensitydetected by the light detection means and of calculating a variation inlight intensity between two successive measurements of light intensity.

Other characteristics, aims and advantages of the invention will emergefrom reading the detailed description which will follow, and withreference to the appended figures, given by way of non-limiting examplesand wherein:

FIG. 1 illustrates a synoptic of the device for detecting gas bubbles ina liquid according to a first arrangement of the light source and thelight detector.

FIG. 2 illustrates a synoptic of the device for detecting gas bubbles ina liquid according to a second arrangement of the light source and thelight detector.

FIG. 3 illustrates a synoptic of the device for detecting gas bubbles ina liquid according to a third arrangement of the light source and thelight detector.

FIG. 4 illustrates a synoptic of an electronic control and processingunit for information according to a first preferred embodiment of theinvention.

FIG. 5 illustrates a synoptic of an electronic control and processingunit for information according to a second preferred embodiment of theinvention.

FIG. 6 illustrates the interfacing of the electronic data controllingand processing unit with a client system within the scope of the firstpreferred embodiment of the invention.

FIG. 7 illustrates the interfacing of the electronic data controllingand processing unit with a client system within the scope of the secondpreferred embodiment of the invention.

FIGS. 1, 2 and 3 illustrate a device according to the present inventioncomprising essentially a light source 1 and a light detector 2 linked toa control and information processing unit 6.

The interfacing of the device with a client system 8 is carried out viaan interface module 7.

As evident from FIGS. 1, 2 and 3, the light is emitted by the lightsource 1 in an illumination zone 4. The field of vision of the lightdetector 2 defines a vision zone 5. And the intersection of the visionzone 5 with the illumination zone 4 defines a zone for detection ofbubbles 3.

The light source 1 can be any type of source, coherent or not, ofelectromagnetic radiation (for example a bright lamp, a light-emittingdiode, etc.). The light detector 2 is any one of conventional lightdetectors (for example photodiode, phototransistor, photoresistance,etc.).

The light detector 2 generates an electric signal 17 in response to aquantity of light originating from the light source 1 and perceived bythe detector 2 in the vision zone 5. This electric signal 17 is thensent to the data controlling and processing unit 6 so that an associatedtime variation can be measured.

Several arrangements of the light source 1 and detector 2 can beadvantageously selected.

The reflection properties of light on the surface of a gas bubble can beutilised within the scope of the invention. FIGS. 1 and 2 illustratethis instance. When no gas bubble is present in the detection zone 3,the light emitted by the light source 1 is perceived only weakly by thelight detector 2. However, when a gas bubble enters the detection zone3, the incident light emitted by the light source 1 is reflected on thesurface of said gas bubble. The reflected light sent by the surface ofsaid bubble is then captured by the light detector 2. The reflectedlight thus creates a variation in the electric signal 17 on theterminals of the light detector 2.

The light source 1 and the light detector 2 can be arranged orthogonallyas illustrated in FIG. 1. The light detector 2 then captures thereflected light in a direction substantially perpendicular to thedirection of incidence of the light emitted by the light source 1.

The light source 1 and the light detector 2 can likewise be arrangedparallel as illustrated in FIG. 2. The light detector 2 then capturesthe reflected light in a direction noticeably parallel to the directionof incidence of the light emitted by the light source 1.

The transmission properties of light in environments (liquid, gas) withdifferent optical characteristics can also be used advantageously.

In this instance and as can be seen in FIG. 3, the light source 1 andthe light detector 2 are arranged opposite each other such that thelight emitted by the source 1 directly strikes the detector 2. Theillumination zones 4 and vision zones 5 are noticeably combined and thedetection zone 3 corresponds to the trajectory borrowed by the lightbetween its emission by the light source 1 and its reception by thelight detector 2.

Different techniques can be selected and especially those relying on theabsorption of a specific wavelength or on the diffraction of light rays.

In particular, a light of a specific wavelength strongly absorbed by oneof the environments (liquid or gas) and weakly absorbed by the otherenvironment can be employed. The wavelength of the light emitted by thelight source 1 in the direction of the light detector 2 can thus bestrongly absorbed by the liquid and weakly absorbed by the gasconstituting the bubbles.

When no gas bubble is present in the detection zone 3, the light emittedby the light source 1 travels through its path in a liquid with strongabsorption coefficient so well that said light is perceived only weaklyby the light detector 2. However, when a gas bubble enters the detectionzone 3, the light emitted by the light source 1 travels through one partof its path in a gas with a low absorption coefficient. The quantity oflight perceived by the light detector 2 when a bubble is present in thedetection zone 3 is then more significant than that perceived by thedetector when no bubble is present in the detection zone 3. It followsthat the passage of a gas bubble into the detection zone 3 creates avariation in the electric signal on the terminals of the light detector2.

The differences in refraction index which exist between the liquid andthe gas constituting the bubbles can also be utilised advantageously.

The light rays emitted by the light source 1 in the direction of thelight detector 2 can be deviated when a gas bubble is present in thedetection zone 5 due to the differences in refraction index which existbetween the liquid and the gas at the level of the surface of thebubbles. The passage of a gas bubble into the detection zone then causesa variation in light intensity perceived by the detector 2, theluminosity at the level of the detector being modified due to thedeviation in light rays.

Moreover, the devices according to FIGS. 1 and 2 for which thereflection properties of the light on the surface of a gas bubble areemployed work only with respect to variations in the electric signal 17generated by the light detector 2. If the sensor constituted by thelight source 1 and the light detector 2 is no longer immersed in theliquid, no variation in the electric signal 17 is in fact detected. Adevice for measuring resistivity of the ambient conditions utilising asystem of electrodes capable of determining whether the electrodes areimmersed in a liquid or in air can advantageously be added to thedevices illustrated by FIGS. 1 and 2. Such a device is described inEuropean patent application EP 1 231 463 which can be used as areference for more information. The incorporation of such a system ofelectrodes makes it possible to obtain a device capable of determiningwhether the sensor is immersed in liquid or not.

When a device according to FIG. 3 employs the absorption properties of aspecific wavelength as has been described previously, no variation inthe electric signal 17 generated by the light detector 2 can be detectedwhen the sensor constituted by the source 1 and the light detector 2 isnot immersed in the liquid. However, in this case, the quantity of lightperceived by the light detector 2 is abnormally high, since the lighttravels through its entire path in a gas with a low absorptioncoefficient. This abnormally high value can then be taken into accountto determine whether the sensor is immersed in liquid or not.

Similarly, when a device according to FIG. 3 employs the diffractionproperties of light rays as has been described previously, no variationin the electric signal 17 generated by the light detector 2 can bedetected when the sensor consisting of the source 1 and the lightdetector 2 is not immersed in liquid. However, the optical materialsutilised can be determined for transmitting maximum light when thesensor is in a gas and a much lower quantity when the sensor is immersedin a liquid. The light rays are effectively bent significantly andconsequently strongly attracted to the light detector 2 when the lighttravels through its entire path in a gas. The light rays are on theother hand slightly bent and consequently weakly attracted to the lightdetector 2 when the light travels its entire path in liquid. Theabnormally high quantity of light perceived by the light detector 2 whenthe sensor is immersed in an ambient conditions constituted by gas todetermine whether said sensor is immersed in liquid or not can then betaken into account.

We will now describe the operation of the data controlling andprocessing unit 6. This is illustrated by FIGS. 4 and 5, whichillustrate respectively the first and the second preferred embodiment ofthe invention.

As is evident from FIGS. 4 and 5, the data controlling and processingunit 6 essentially comprises a control module 15 of the light source 1,an analog/digital conversion module 11 capable of digitising theelectric signal 17 generated by the light detector 2 and a module forprocessing the light intensity in the detection zone of the bubbles 3.

The electric signal 17 generated by the light detector 2 in response tothe quantity of light it perceives is digitised via the analog/digitalconversion module 11.

The control of the light source 1 must be active during the acquisitionof the corresponding signal of the light intensity perceived by thelight detector 2. The control of the source is carried out by thecontrol module 15 of the light source and is either continuous or, as isthe case within the scope of the description, pulsed and synchronisedwith the acquisition via a synchronisation module 14.

The control module 15 of the light source is capable of polarising thelight source 1 periodically and of measuring the electric signal 17collected on the light detector 2. The polarisation can be performed onseveral levels for optimum regulation of the intensity of the lightemitted. This calibration is carried out typically by successivelytesting the possible polarisation values of the light source and byretaining the polarisation value having given the best voltage of theelectric signal 17 collected on the light detector, that is, the bestaligned voltage in the possible range of voltage. This calibration iscarried out at regular intervals to compensate for the deviations of theoptical characteristics of the system (soiling, opacification, etc.) aswell as those due to variations in temperature. The time interval istypically between 10 s and 1 min. It thus appears that an advantage ofthe invention lies in the fact that the deviations of the system do notaffect the sensitivity of the device used by the invention.

As mentioned previously, the detection of the presence of a gas bubblein the detection zone 3 is carried out by measuring the variation inlight intensity perceived by the light detector 2. The time scale formeasuring these variations must correspond to the average time taken bya bubble to travel through the detection zone 3, which depends on thesize of the detection zone and the velocity of the bubbles to bedetected. Typically, the time constant is between a few hundredmicroseconds and a few milliseconds for a velocity of a few metres persecond.

A device for measuring temperature such as that already been describedin European patent application EP 1 231 463 to which can be used as areference for more information can advantageously be added to the deviceaccording to the present invention. The incorporation of such a devicemakes it possible to provide a two-function sensor (temperature of theliquid/presence of gas bubbles in the liquid). As known, a temperatureprobe which can be short-circuited when the device has detected thepresence of bubbles can be utilised.

As seen previously, when the sensor constituted by the light source 1and the light detector 2 is not immersed in liquid, it is impossible todetect the absence of liquid by measuring the variation in lightintensity. The observation via the control module 15 of the light sourceof the polarisation value of the light source 1 makes it possible toalert the client system to the problem and to substitute the main alarmsystem.

As mentioned above, when the sensor is not immersed in the liquid, theenvironment effectively transmits much more light than under normalcircumstances. The polarisation value of the light source consequentlytakes an abnormally low value. An overshoot detector 16 of a predefinedpolarisation threshold makes it possible to detect whether the sensorconstituted by the source and the light detector is immersed in liquidor not.

The client system 8 is then alerted via the interface module 7 of thetotal absence of liquid at the level of the sensor when the polarisationvalue of the light source 1 is lower than a predefined threshold value Tand is detected as such by the overshoot detector 16 of a predefinedpolarisation threshold.

This substitute can however be put to use only within the scope ofcapture technologies by transmission (especially absorption of aspecific wavelength and diffraction of light rays on the surface of abubble) described previously and illustrated by FIG. 3.

Within the scope of capture technologies by reflection describedpreviously and illustrated by FIGS. 1 and 2, analysis of the variationsbetween two successive measurements of the light intensity perceived bythe light detector 2 cannot detect whether the sensor is immersed in theliquid or not. In order to make this detection feasible, it is possibleto add to the device a system of electrodes as has been describedpreviously. In this way the principal alarm system can be substitutedfrom when the sensor is no longer immersed in the liquid.

According to a first preferred embodiment of the invention, theprocessing module 9 for light intensity comprises logical comparisonmeans 12 capable of detecting any notable variation in light intensitybetween two successive measurements, as well as statistical processingmeans 21 of said variation capable of providing information on whetheror not the limited bubble content has been exceeded.

Said logical comparison module 12 is constituted by means 18 capable ofcalculating the variation in light intensity between two successivemeasurements made at the level of the light detector 2 and means 19capable of detecting whether a predetermined threshold S has beenexceeded.

In the absence of bubbles, the successive measurements of lightintensity are identical. The passage of a bubble in the detection zone 3modifies the light intensity perceived by the detector 2. Thismodification of light intensity in the detection zone 3 is conveyed by avariation in the electric signal 17 on the terminals of the lightdetector 2. It is these time variations which are detected.

The variation in light intensity is then calculated by comparing, viameans 18, the value of the electric signal 17 to that previouslyobtained. The measurement of variation in light intensity between twosuccessive measurements is then compared to a predetermined threshold Svia the means 19 for detecting a threshold exceeding. If the differencebetween these two successive values is greater than the threshold S, thesystem considers that a bubble is present in the detection zone 3.

In the event of the threshold S being exceeded, the warning counter 13of the statistical processing means 21 of the variation betweensuccessive measurements of light intensity is incremented by apredetermined value A. Otherwise, this same counter is decremented by avalue B. The values A and B are such that A is greater than B and theirA/B ratio is generally between 10 and 1000.

The warning counter 13 is delimited between two predefined values. If itgoes beyond an alarm value C, the data controlling and processing unit 6would then inform the client system 8 via the interface module 7 thatthe bubble content is greater than the authorised limited content. Saidvalue C is generally between 70% and 95% of the maximum value of thewarning counter 13.

To optimise the system, an hysteresis can be set up by means of a finalalarm value D which avoids the transitory problems between the twooutput states.

The values C and D are fixed such that C is greater than D. According tothe cases, the A/C ratio is typically between 1/25 and 1/250 and the D/Cratio typically between 3/10 and 8/10.

A time delay can likewise be added to the system to advantageouslyincrease the functional enhancement of the detector. The choice can bemade for example to trigger the alarm only if the warning counter 13exceeds the alarm value C′ over a period greater than the time delayvalue. The value C′ is generally, though not compulsorily, equal to C.

One of the advantages of data processing carried out within the scope ofthis first preferred embodiment of the invention lies in the fact thatthe response time is inversely proportional to the quantity of bubblespresent in the detection zone. A highly significant presence of bubblesis detected very rapidly, whereas a small quantity is analysed longerand more precisely in order to ensure that the detection is founded. Anyfalse alarm is thus avoided.

According to a second preferred embodiment of the invention, theprocessing module 22 of light intensity comprises means 18 capable ofcalculating the variation in light intensity between two successivemeasurements as well as means 23 capable of extracting the average valuefrom a plurality of said variations between two successive measurementsof light intensity.

The variation in light intensity is calculated by comparing, via themeans 18, the value of the electric signal 17 previously digitised bythe analog/digital conversion module 11 to the value previouslyacquired. The measurement of the variation in light intensity betweentwo successive measurements is then introduced into a low-pass numericalfilter characterised by its coefficients Fo and constituting means 23capable of extracting the average value from the variations between twosuccessive measurements of light intensity.

The data controlling and processing unit 6 then sends the client system8, via the interface module 7, this average value which isrepresentative of the bubble content in the liquid.

This second preferred embodiment of the invention makes it possible toindicate reactively the quantity of bubbles present in the liquid. Itthus offers a flexibility of use to the client who can regulate orre-regulate the system when desired, even elaborate new alarmstrategies, by utilising pre-alarm levels for example.

As seen previously, a temperature measuring device can advantageously beadded to the device according to the present invention. A temperatureprobe which can be short-circuited when the sensor has detected thepresence of bubbles and/or when the sensor is not immersed in the liquidcan be utilised.

The incorporation of such a temperature measuring device makes itpossible to provide a three-function sensor (temperature ofliquid/presence of gas bubbles in the liquid/absence of liquid) whencapture techniques based on the transmission properties of light inenvironment having different optical characteristics are employed.

The incorporation of such a temperature measuring device makes itpossible to provide a two-function sensor (temperature ofliquid/presence of gas bubbles in the liquid) when capture techniquesbased on the reflective properties of light on the surface of gasbubbles are employed. If, as has been seen previously, a system ofelectrodes is furthermore incorporated, the third functionality (absenceof liquid) is advantageously added to the device according to theinvention.

The interfacing with the client system 8 can advantageously be carriedout, as is illustrated by FIGS. 6 and 7, by utilising only a singleconnection wire simultaneously carrying information concerning thetemperature of the liquid, the presence of bubbles in the liquid and,according to certain configurations, the absence of liquid.

FIG. 6 illustrates such interfacing within the scope of the firstpreferred embodiment of the invention, When the sensor has detected thepresence of bubbles or the absence of liquid, an alarm signal isgenerated. This alarm signal controls the short-circuiting of thetemperature probe. In such a way, the outgoing signal for the clientsystem 8 is at a high-amplitude level proportional to the temperature ofthe liquid when the sensor is immersed in the liquid and when no bubbleis detected in the detection zone. Said signal takes a low levelfollowing short-circuiting of the probe when the sensor has detected thepresence of bubbles or the absence of liquid.

The FIG. 7 illustrates the interfacing which can be carried out withinthe scope of the second preferred embodiment of the invention. Atregular intervals information on the bubble content is sent in the formof a train of PWM strobes (Pulse Width Modulation or in FrenchModulation de Durée et d'Impulsion). For this, the value of the voltageof the variable resistance forming the temperature measuring device isperiodically pre-set to the ground and feeder voltage of the sensor. Thewidth of the pulses is proportional to the measured bubble content. Anabsence of liquid at the level of the sensor is considered as a maximumbubble content and is thus illustrated by a train of pulses of maximumwidth. The output signal for the client system 8 is thus constituted bythe periodic succession of a constant high-amplitude signal levelproportional to the temperature of the liquid and a PWM signalrepresentative of the bubble content in the liquid.

As indicated previously, the invention applies in particular, though notexclusively, to the detection of gas bubbles in a cooling circuit of aninternal combustion engine of a motor vehicle.

For this purpose, it is noted that the parameters A, B, C, C′, D, S, T,the coefficients of the filter (Fo), as well as the frequency at whichacquisitions are made can be regulated according to the characteristicsof the system to be monitored. Action can thus be taken especially onthe response time, the sensitivity in accordance with the velocity ofthe bubbles, etc.

Of course, the invention is not limited to the particular embodimentswhich have just been described, but extends to any variant in keepingwith its spirit.

1. Process for detection of gas bubbles in a liquid adapted to a devicecomprising a light source (1), a light detector (2) and a datacontrolling and processing unit (6) linked to a client system (8)comprising the steps of emitting light from the light source (1), foracquisition of the successive measurements of light intensity perceivedby the light detector (2) and for calculation of a variation between twosuccessive measurements of said light intensity.
 2. Process according toclaim 1, characterised in that it further comprises a comparison step ofthe time variation at a predefined threshold value S.
 3. Processaccording to claim 2, characterised in that it further comprises anincrementation step of an alarm counter (13) by a predefined value Awhen the variation in light intensity perceived by the light detector(2) between two successive measurements is greater than the threshold Sand decrementation of said warning counter (13) by a predefined value Bin the opposite case.
 4. Process according to claim 3, characterised inthat it further comprises a step of sending to the client system (8)information indicating that a bubble content is greater than anauthorised maximum content when said warning counter (13) exceeds apredefined value C known as the alarm value.
 5. Process according toclaim 3 characterised in that it further comprises a step consisting ofsending to the client system (8) information indicating that a bubblecontent is greater than an authorised maximum content when said warningcounter (13) exceeds a predefined value C′ known as the alarm value overa period greater than a predefined time delay period.
 6. Processaccording to any of claims 4 or 5 characterised in that it furthercomprises a ceasing step of sending to the client system (8) informationindicating that the bubble content is greater than the authorisedmaximum content when the warning counter (13) is less than a predefinedvalue D known as the final alarm value.
 7. Process according to claim 1,characterised in that it further comprises a calculation step of anaverage value from a plurality of variations between two successivemeasurements of light intensity.
 8. Process according to claim 7characterised in that it further comprises a step of sending to theclient system (8) information indicating the average value of thesuccessive variations of the light intensity perceived by the lightdetector (2).
 9. Process according to any of the above claims,characterised in that the data controlling and processing unit (6)comprising a control module of the light source (15) capable ofpolarising said light source (1) on several polarisation levels, thelight source (1) is polarised periodically by said control module (15)of the light source.
 10. Process according to claim 9, characterised inthat a calibration of the sensor constituted by the source (1) and thelight detector (2) is carried out synchronously on the periodicpolarisation of the light source (1).
 11. Process according to any ofthe above claims, characterised in that the source (1) and the lightdetector (2) being arranged noticeably orthogonally, the acquisitionstep of the successive measurements of light intensity perceived by thelight detector (2) makes it possible to acquire measurements of thequantity of light rays emitted by the light source (1) which arereflected should the case arise in the presence of bubbles on thesurface of a gas bubble in a direction noticeably orthogonal to thedirection of incidence towards the light detector (2).
 12. Processaccording to any of claims 1 to 10, characterised in that, the source(1) and the light detector (2) being arranged noticeably adjacently, theacquisition step of the successive measurements of light intensityperceived by the light detector (2) makes it possible to acquiremeasurements of the quantity of light rays emitted by the light source(1) which are reflected should the case arise in the presence of bubbleson the surface of a gas bubble in a direction noticeably parallel to thedirection of incidence towards the light detector (2).
 13. Processaccording to any of claims 11 or 12, characterised in that, the devicelikewise comprising a temperature measuring element and at least oneswitch linked to said temperature measuring element, the switch iscapable of changing state during the detection of a gas bubble. 14.Process according to claim 13, characterised in that, the datacontrolling and processing unit (6) transmitting, via an interfacemodule (7), to the client system (8) information on the temperature ofthe liquid and the presence of gas bubbles in the liquid, the interfacemodule (7) and the client system (8) being linked only by a single wire,a high-amplitude level signal proportional to the temperature of theliquid when the presence of a bubble is not detected or low level whenthe presence of a bubble is detected is sent to the client system (8) bythe interface module (7).
 15. Process according to any of claims 11 or12, characterised in that, the device likewise comprising a system ofelectrodes capable of measuring the resistivity of the ambientconditions and since the data controlling and processing unit (6) beinglinked to the client system (8) via an interface module (7), the clientsystem (8) is informed, via the interface module (7), by the datacontrolling and processing unit (6), that the sensor constituted by thesource (1) and the light detector (2) is not immersed in the liquid whenthe system of electrodes identifies the ambient conditions as not beingthe liquid.
 16. Process according to claim 15, characterised in that,the device likewise comprising a temperature measuring element and atleast one switch linked to said temperature measuring element, theswitch is capable of changing state during the detection of a gas bubbleand during the absence of liquid.
 17. Process according to claim 16,characterised in that, the data controlling and processing unit (6)transmitting, via the interface module (7), to the client systeminformation on the temperature of the liquid, the presence of gasbubbles in the liquid and the non-immersion of the sensor in the liquid,the interface module (7) and the client system (8) being linked only bya single wire, a high-amplitude level signal proportional to thetemperature of the liquid when the presence of a bubble is not detectedand when the sensor is immersed in the liquid or low level when thepresence of a bubble is detected or when the sensor is not immersed inthe liquid is supplied to the client system (8) by the interface module(7).
 18. Process according to any of claims 1 to 10, characterised inthat, the source (1) and the light detector (2) being arrangednoticeably opposite each other, the step of light emission makes itpossible to send out a light of specific wavelength from the lightsource (1) such that it is strongly (reciprocally weakly) absorbed bythe liquid and slightly (reciprocally strongly) absorbed by the gasconstituting the bubbles.
 19. Process according to any of claims 1 to10, characterised in that, the source (1) and the light detector (2)being arranged noticeably opposite each other, the acquisition step ofthe successive measurements of light intensity perceived by the lightdetector (2) makes it possible to acquire measurements of the quantityof light rays emitted by the light source (1) which are deflectedtowards the light detector (2) should the case arise in the presence ofbubbles due to the diffraction index differences between the liquid andthe gas constituting the bubbles at the level of the surface of saidbubbles.
 20. Process according to any of claims 18 or 19, characterisedin that, the device likewise comprising a temperature measuring elementand at least one switch linked to said temperature measuring element,the switch is capable of changing state periodically.
 21. Processaccording to claim 20, characterised in that, the data controlling andprocessing unit (6) transmitting, via an interface module (7), to theclient system information on the temperature of the liquid and thepresence of bubbles in the liquid, the interface module (7) and theclient system (8) being linked only by a single wire, a periodic signalis supplied to the client system (8) by the interface module (7). 22.Process according to claim 21, characterised in that the period of saidperiodic signal is formed by a first phase constituted by a constanthigh-amplitude level signal proportional to the temperature of theliquid and by a second phase constituted by a train of pulses ofmodulated width, the width of the impulses being modulated according tothe average value of the successive variations in light intensityperceived by the light detector (2).
 23. Process according to any ofclaims 18 or 19, characterised in that the client system (8) isinformed, via an interface module (7), that the sensor is not immersedin liquid when the polarisation value of the light source (1) is lowerthan a predefined threshold value T, known as the polarisation alarmthreshold value.
 24. Process according to claim 23, characterised inthat, the device likewise comprising a temperature measuring element andat least one switch linked to said temperature measuring element, theswitch is capable of changing state periodically.
 25. Process accordingto claim 24, characterised in that the data controlling and processingunit (6) transmitting, via the interface module (7), to the clientsystem the information on the temperature of the liquid, the presence ofbubbles in the liquid and the non-immersion of the sensor in the liquid,the interface module (7) and the client system (8) being linked only bya single wire, a periodic signal is supplied to the client system (8) bythe interface module (7).
 26. Process according to claim 25,characterised in that the period of said periodic signal is formed froma first phase constituted by a constant high-amplitude level signalproportional to the temperature of the liquid and a second phaseconstituted by a train of pulses of modulated width, the width of theimpulses being modulated according to the average value of thesuccessive variations in light intensity perceived by the light detector(2) and said width being maximum when the sensor is not immersed in theliquid.
 27. Device of detection of gas bubbles in a liquid comprisinglight emission means, light detection means and data controlling andprocessing means linked to the light detection means, characterised inthat following emission of light by the light emission means andfollowing the detection of light by the light detection means, the datacontrolling and processing means are capable of obtaining lightdetection means of the successive measurements of light intensitydetected by the light detection means and of calculating a variation inlight intensity between two successive measurements of light intensity.